An internal rotating inspection system (IRIS) is an immersion ultrasonic non-destructive testing (NDT) system used to measure the wall thickness or inspect the wall conditions of tubular materials, in particular for, but not limited to, heat exchanger tubing and boilers. IRIS technology is often used to confirm and provide sizing of outside diameter (OD) or internal diameter (ID) defects, such as multiple pit clusters.
An IRIS C-scan view is a succession of IRIS B-scans representing one probe turn. The B-scan is alternatively represented in a cylindrical view, which puts more into evidence the importance of probe centering. While the IRIS probes detect OD and ID pitting relatively easily by means of the B-scan view, the screening of the multiple defects in a C-scan view is a tedious process, and can lead to missing defects as errors are inevitable.
The C-scan view offers a color-coded display of the local ID value or the OD value. However in practice, the centering of the IRIS probe is virtually never perfect, and, more than often, significantly off-centered. This has the effect of shifting the whole color spectrum of ID or OD C-scan views, and hiding the defects that may be pushed outside the effective color range for detection.
While OD pits can be easily represented in a C-scan view by means of a “wall thickness” C-scan, ID pits cannot use such compensation; therefore the identification of ID pits in a C-scan view is very much dependent on probe centering.
Moreover, IRIS probe centering dynamically changes several times, in random moments, during the inspection. As a result, a simple ID defect analysis cannot be done. Standard practice is to find the deepest defect, yet an analyst must select each and every defect, measure or estimate its depth, take notes, and find the deepest one. This is a tedious process as many as several hundred defects can be found in tubes.
Some existing probe-centering methods inside a tubular testing material are used in existing practice. U.S. Pat. No. 5,329,824 discloses a probe-centering method of using multiple bendable support legs that are pivotally connected at different points to an inspection device inside a tube. U.S. Pat. No. 4,597,294 discloses a probe positioning system inside a tube using an oscilloscope, cam lock assemblies, and a predetermined axial extent from a magnetic tape recorder. However these solutions to centering a probe are mechanical, and do not have the precision offered by software working directly with the IRIS probe.
Considering the background information above, a solution that automatically centers an IRIS probe for C-scans would be of great economic value. It would be possible to obtain the same inspection and analysis results with existing IRIS equipment and software, but more intuitively and in a much faster way. An analyst could instantly locate the deepest defects and speed up the analysis, once the color palette has been properly adjusted. This would allow huge time savings while increasing the probability of detection, and also add further confidence in the IRIS technology or system being sold by a manufacturer.